thinkphp的模版引擎，把渲染结果返回到变量中，而不直接输出到浏览器.
想用来整理渲染html转PDF
public function index()
{
ob_start();//打开缓冲区输出
$html = View::fetch();
ob_end_flush();
return $html . "OK";
}
原理是在要输出浏览器的部分使用ob清除掉。
1、页面调整
redirect('/admin/index')->send();
参考文档：https://www.kancloud.cn/manual/thinkphp6_0/1037481
一、安装Composer
curl -sS https://getcomposer.org/installer | php mv composer.phar /usr/local/bin/composer
二、安装稳定版thinkphp
在WEB的根目录运行以下指令
composer create-project topthink/think tp
he Process class relies on proc_open, which is not available on your PHP installation. The archive may contain identical file names with different capitalization (which fails on case insensitive filesystems) Unzip with unzip command failed, falling back to ZipArchive class
putenv() has been disabled for security reasons
安装成功！
